The present invention relates to sports racquets, for example tennis, squash, badminton, and racquetball racquets. Such racquets have a head portion containing an interwoven string bed, a handle, and a shaft portion connecting the head portion to the handle.
In conventional racquets, holes for anchoring the ends of the strings are formed in the frame by drilling small string holes in the frame after the racquet is molded. Generally, each string hole accommodates a single string. Plastic grommet pegs, which are formed on a grommet strip that extends along the outside surface of the frame, extend through the string holes to protect the strings from the sharp edges of the drilled holes.
Co-owned PCT application WO 2004/075996 discloses a sports racquet in which some adjacent pairs of small string holes along the sides, tip, and throat bridge of the racquet are replaced by enlarged string holes, the opposite ends of which each accommodates one string (referred to herein as “port string holes”). Preferably the frame is formed of a double tube of carbon fiber-reinforced composite material (a so-called graphite frame), in which the enlarged string holes are molded into as the racquet as the racquet is pressure molded. As a result of using two tubes, each forming one-half of the enlarged string hole, the string holes can have rounded edges and do not require the use of grommet pegs or strips. Also, in the regions between string holes, the adjoining walls of the two tubes are bonded together to form an internal stiffening wall lying in the plane of the string bed. The result is a racquet which has improved torsional stiffness and lighter weight.
The playing characteristics of a graphite sports racquet can be changed in various ways, such as by changing the geometric shape of the frame, the materials used, the number and fiber orientation of the various plies of composites used at each racquet location, or the frame's overall weight, balance, stiffness, and polar and mass moments of inertia. While racquet designers currently have substantial latitude in designing the various playing characteristics of a racquet, it would be desirable to allow for even greater flexibility in the ability to design a new racquet's playing characteristics.